Underground manholes and the like are frequently formed from brick, cement, and like cementitious and/or refractory materials. The manhole usually has a relatively long neck portion extending from the surface, and terminating in a lower sometimes flaring portion to which a sewer pipe communicates. The sewage flowing through the sewer pipe may, over time, damage the mortar which secures the bricks of the manhole together, or the cement with which the manhole is formed. Damage to the bricks and cement will permit ground water and subsurface water to infiltrate the manhole, with the result that the water treatment plant may become overloaded and unable to handle the amount of water which it receives during rain and other such occurrences. In that event, either untreated water is uncontrollably discharged, or the water treatment plant itself becomes unable to perform its function and needs to be taken out of service.
Replacement of a manhole is a relatively expensive undertaking, because of the need to excavate the surrounding soil, and remove the bricks and other materials. In addition, the sewer itself must continue to be usable during the procedure, or else homes and businesses will be unable to flush toilets, run taps, etc. For this reason, it is desireable to rehabilitate and/or reinforce the manhole in a way which avoids a need for replacement.
My prior patent, U.S. Pat. No. 5,265,981, issued Nov. 30, 1993, the disclosure of which is incorporated herein by reference, discloses a method and apparatus for rehabilitation a manhole through use of a resin impregnated fiberglass liner which is inflated and cured in place while permitting the manhole to remain in service as it is being rehabilitated. That patent discloses the use of heated air to inflate the liner so that the surrounding walls of the manhole are engaged, after which the resin cures and secures the liner to the walls of the manhole. I have found that heated air can take a relatively long period to achieve sufficient resin cure. Particularly for deep manholes, the walls of the manhole and the surrounding soil act as a heat sink which tends to cool the resin, so that additional time for curing is required because the surrounding material also must be heated somewhat.
In view of the above, those skilled in the art will understand that there is a need for a method and apparatus which inflates the manhole liner and achieves cure of the resin more rapidly than may be accomplished through use of heated air alone. The disclosed invention meets these needs through the simultaneous introduction of pressurized, heated air and steam through a common conduit creating an extremely turbulent condition within the inflated liner and causing the inflated liner to resemble a convection oven.